Sensor systems such as magnetoresistive (MR) sensor modules provide a simple and cost effective solution for providing rotational speed measurement in both automotive and industrial applications. They typically consist of a magnetoresistive sensor element, a permanent magnet fixed to it and an integrated signal conditioning circuit. Relevant aspects such as mounting, electrical properties and possible encapsulation are important considerations for their use.
Angular and linear position sensors are widely used in automatic control systems as feedback-sensing devices in one or more control loops of the system. Various types of angular position sensors are currently used in the automobile industry in conjunction with vehicle steering wheels, or hand wheels, including relative, absolute, analog and digital angular position sensors. Known technologies that can be used to determine angular position include contact measurement, such as a resistance stripe, or non-contact measurement effects, based on inductance, capacitance, optical, or magnetic field. A relative angular position sensor measures the angular position of a rotating object by either incrementing or decrementing a counter, depending upon the rotational direction of the object, and relating that information to an angular reference point. Rotary position sensing is used in a number of applications, such as motor position feedback control and/or commutation, cam and crank shaft position sensing for controlling ignition timing, misfire detection, engine speed monitoring etc, robotics, and machine tool position control. Rotary position sensors utilize a magnetic field and a magnetosensitive device, such as a Hall effect device or a magnetoresistor located within the magnetic field. Absolute position sensors provide a sensed position signal which contains information about the absolute position relative to a predetermined position. An absolute position sensor indicates very precisely the position of the moving components, so that they can be controlled and, above all, so that these components can be relocated when the system in which they are integrated is activated. An absolute position sensor delivers a number of output signals in the case of a parallel digital output signal, but in the case of a series digital output signal, the sensor delivers a single signal resulting from a shaping according to a data transmission protocol and executed from the signals in parallel described in therein.
A 2-wire digital current output sensor for automotive manufacturers, the IX MR magnetoresistive wheel-speed sensor from Honeywell Sensing and Control, Freeport, Ill., can sense multiple ring magnets found in smart bearings, offering a one pulse per pair output. The system interfaces with typical electronic control unit modules for antilock braking systems; its low-gauss operation works over large sensing distances.
Magnetoresistive (MR) speed sensors are ideal for sensing the speed of an input or output shaft of an automatic transmission. The sensor is typically mounted in association with a transmission control unit (TCU). Angular Position Sensors, such as ratiometric MR sensors, are ideal for sensing the angle position of transmission components in the shift linkage of a transmission and are also mounted in association with a transmission control unit (TCU).
Among position sensing technologies, magnetic sensing is known to have a unique combination of long life components and excellent resistance to contaminants. Magnetic sensors typically rely upon permanent magnets, typically ferrite-based, to detect the presence or absence of a magnetically permeable object within a certain predefined detection zone relative to the sensor. In combination with the permanent magnet, some sensors of this type utilize magnetoresistive components located at particular positions relative to the permanent magnet and other. Generally, a magnet is used to create a magnetic field which is measured by an IC (integrated circuit) containing a magnetically sensitive feature. The magnet is connected to the element to be measured. The changing magnetic field at the IC caused by the interaction of the magnet with forces being measured is converted into an output signal proportional to the movement.
Magnetoresistive sensors are a type of magnetic sensor that uses the magnetoresistive effect to detect a magnetic field. Ferromagnetic metals, such as the nickel-iron alloy commonly known as Permalloy, alter their resistivity in the presence of a magnetic field. When a current is passed through a thin ferromagnetic film in the presence of a magnetic field, the voltage will change. This change in voltage represents the strength or direction of the magnetic field. Some magnetic position sensors provide an indication of the displacement of the mechanical component by using a magnetic field sensing device which reports the intensity of a magnetic field from a magnet which is positioned on the mechanical component. The magnet is positioned and the magnetic field sensing device is located relative to the magnet in such a fashion as to cause the magnetic field to vary in the magnetic field sensing device as the magnet moves.
Magnetic position sensors are a non-contact type of sensor which are devices that generate change to an electronically interrogated physical parameter that is proportional to the movement of a structure, such as, for example, an actuator shaft operatively coupled to the sensor. This change is achieved without physical contact between the parameter and the interrogation device. Magnetic position sensors consist of a magnetic field sensing device which is usually stationary and a magnet that is attached to a moving component. As the magnet approaches the sensing device the magnetic field of the magnet is detected and the sensing device generates an electrical signal that is then used for counting, display, recording and/or control purposes. In magnetic position sensing, the magnitude of magnetic field strength is generally measured by an appropriate measuring device, such as a magneto-resistive element. The value of the measured field intensity is translated through the measuring device to a voltage or current value that is uniquely representative of the specific rotational position of the actuator shaft.
One of the benefits of using magnetic sensors is that the output of the sensor is generated without the use of contacts. This is a benefit because over time contacts can degrade and cause system failures. Because such a position sensor bases positional detection on magnetic properties, this type of sensor inherently excels in resistance to exposure to common environmental contaminants such as water, oil, etc.
Referring to FIG. 1, a magnetoresistive (MR) sensor 100 is composed of a transducer 110 and a magnet 120 mounted within a housing 105. The housing 105 has a sensing face 115 where measurements are directly received by the sensor 100. An electrical connector 130 is also typically disposed on the housing 105 opposite the sensing face 115. A flange 140 is snuggly located around the outer surface of the housing 105 between the electrical connector 130 and sensing face 115. The flange 140 includes integrated mounting hardware 150, such as a brass bushing, which is used to fixably mount the MR sensor 100 to a system being monitored (not shown). A problem with MR sensors is encountered during manufacturing. A MR sensor may be manufactured for particular use specifications in mind. A MR sensor's magnet can be located at various distances relative to a sensing face, which causes the MR sensor to react differently for given applications. Referring again to the prior art MR sensor illustrated in FIG. 1, what is important to note is that the magnet 120 is mounted within the housing 105 at a fixed distance “X” from the sensing face 115 of the MR sensor 100. This distance dictates the type of sensing or sensing that will be accomplished by the MR sensor 100. Referring now to FIG. 2, a sensor similar in shape and hardware is as shown in FIG. 1 is shown. The MR sensor in FIG. 2, however, shows that the magnet is located at a new distance “Y” from the sensing face. The new distance determines that this sensor is used for a different application than the MR sensor in FIG. 1.
As described in the background as a common problem with sensors that are similar in size and look, but required for different uses, it is hard to determine the type of sensor that is embodied within the similar looking housing after manufacturing is accomplished. A need to overcome this limitation is required.
The present inventors present a system that can overcome limitations found in the art. The present inventors teach that two sensors can be built with the same form and fit (physically are the same shape), but require different magnetic calibration for an application target wheel. Normally under this scenario, the parts are kept segregated so they don't end up being used in the wrong application.